06/02/2003

Stoichiometric means a chemical balance of oxygen and fuel.  Nothing zip nada
else.  Any other meaning is not supported by fact and is probably an internet
fiction.

For normal hydrocarbons burning in air:

Stoichiometric is where the peak energy release per unit mass of fuel occurs.

Peak flame temperature occurs about 5 - 10% rich of stoichiometric.  This is
due to the deliberate sacrifice of the energy in carbon for the energy in
hydrogen.  This results is the maximum number of small particles - a process
called dissociation. CO and CC is lighter than CO2 and therefore will have a
higher temperature.  This correlates with knock as knock occurs at the highest
temperature.  This also correlates with peak exhaust gas temperature.

In all rich mixtures, the total energy PER UNIT MASS of fuel goes down from
stoichiometric upwards.  As a rule - the flame speed increases as you go
excess fuel up to about 40% or so.  This is because more free hydrogen is
available and free hydrogen burns hotter, faster - about 8 to 9 times faster
than gasolines and with more air - 1000% ( One THOUSAND percent ) excess air
vs gasolines limit of about 25% excess air.

All fuel added above peak temperature mixture functions SOLEY as an internal
coolant.

As you go lean of Stoichiometric, the total energy decreases.  The flame
temperature decreases.  The flame speed falls off.  

Lean, although we are losing energy and speed, we are gaining mass.  Lean best
power is where we have gained the most mass possible and lost a minimum of
energy - thus making the highest bmep of a given unit of fuel.

Going lean requires advancing the spark to maintain the same bmep because the
speed is slower.

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To the best that I can tell from research papers and practical experience.  It
appears to be around the amount of free hydrogen at the time of combustion.  

Non normal hydro-carbons - nitro compounds in particular - have strong
internal energy bonds and when these break down has a major effect on speed.
Even though nitromethane burns hundreds of degrees hotter than normal
hydrocarbons - it burns SLOWLY because its oxygen in not released until way
late in the cycle.

Slow burning is particularly associated with light loads and lean mixtures.
Lean misfire is the engine running out of time before combustion completes.

The flame speed data I have seen tends to agree with that.  But the big fall
off on flame speed starts slightly lean of stoic.

Side different note.  I am trying Cetane Improver to raise the speed of cruise
mixtures to enable both lean and low pressure.  Blending it in the tank is
fast and dirty and not by any definition optimal.  Overdid it and cost me a
gallon of pure xylene.

The normal methodology for lean mixtures is to add timing to break the peak
pressure back to where its supposed to be.  The German R-Fluid method was to
introduce an ignition accelerator instead of timing.  The reasoning was the
whole combustion curve gets moved with timing, but, by accelerating
combustion, the energy release gets tightened nearer tdc - thus reducing the
whole amount of energy needed.